1. Field of the Invention
The invention pertains to the field of keratoplasty and, more particularly, to systems and methods for stabilizing corneal tissue after treatment of the corneal tissue.
2. Description of Related Art
A variety of eye disorders, such as myopia, hyperopia, astigmatism, and keratoconus involve abnormal shaping of the cornea. Keratoplasty reshapes the cornea to correct such disorders. For example, with myopia, the shape of the cornea causes the refractive power of an eye to be excessive. Parallel rays of light are focused in front of the retina, producing a blurred image of objects at a distance. Flattening aspects of the cornea's shape about the visual axis through keratoplasty decreases the refractive power of an eye with myopia and causes the image to be properly focused at the retina.
In another example, with hyperopia, the shape of the cornea causes the refractive power of an eye to be insufficient. Parallel rays of light are focused behind the retina, producing a blurred image of objects proximate to the eye. Steepening or bulging aspects of the cornea's shape about the visual axis through keratoplasty, such as by removing a ring of tissue from the outer edge of the cornea, increases the refractive power of the eye, and causes the image to be properly focused at the retina.
With astigmatism and keratoconus, the surface of the cornea or the lens behind the cornea is not spherically shaped, and is instead shaped irregularly. An astigmatic eye is often shaped like the back of a spoon, causing parallel rays of light to focus at two separate points, creating a distorted image, and can accompany hyperopia or myopia. A keratoconus eye has more of a conical shape than a normal, gradual curve. In order to cause the image to be properly focused at the retina, the cornea can be given an overall more spherical shape using keratoplasty. For example, with respect to keratoconus, the abnormally steep curves in the cornea can be flattened.
Invasive surgical procedures, such as laser-assisted in-situ keratomileusis (LASIK), may be employed to reshape the cornea. However, such surgical procedures may typically require an extended healing period after surgery. Furthermore, such surgical procedures may involve complications caused by the cutting of a flap in the cornea to provide access to the stromal layer, such as dry eye syndrome caused by the severing of corneal nerves.
Many other serious, risky complications may arise in LASIK due to the cutting of the flap, such as striae, ectasia, buttonhole flap, and free flap. For example, striae, or wrinkles in the corneal flap, can occur following surgery due to the improper replacement of the flap during surgery and/or movement of the flap caused by normal activity post-surgery. Although it does not require correction in some cases, in others surgical correction is necessary to re-lift and smooth the flap.
In ectasia, the corneal flap is cut too deep and/or too much tissue is removed, causing the remaining corneal tissue can become too thin. The thinness of corneal tissue can cause it to weaken under normal, everyday pressure, causing it to bulge or deform. Such deformation can itself cause residual myopia and astigmatism that may require contact lenses to be worn despite the LASIK surgery. In severe cases, a corneal transplant may be necessary.
Buttonhole flap can also result from corneal flap cutting, which refers to a tear, uneven cut or rip in the flap. This can be caused by a variety of factors, including improper placement of the blade, the use of an excessively worn blade, or the use of an improperly sized blade. In other cases, the flap rips when it is placed back over the eye at the end of surgery. This can result in astigmatism and scarring that can worsen vision beyond its original state, and requires surgical correction once the flap has time to heal, usually around 6 months post-op.
Free flap is caused by the complete removal of the corneal flap. In other words, no connecting hinge is maintained between the flap and the eye. This can be caused by a loss of suction at the blade as it is creating the flap or by operator error. In some cases, the surgery can be completed as usual and the flap replaced without the hinge. However, this may increase the risk of other flap complications such as striae or buttonhole flap resulting from the increased handling required to remove and replace the flap without a hinge. In addition, the flap can suffer irreparable harm or be lost entirely, requiring that a corneal transplant be performed on the patient.
Thermokeratoplasty, on the other hand, is a noninvasive procedure that eliminates the need to cut a flap in the eye to correct corneal abnormalities. Thermokeratoplasty may be used to correct the vision of persons who have disorders associated with abnormal shaping of the cornea, such as myopia, hyperopia, astigmatism, and keratoconus, as described above. Thermokeratoplasty may be performed by applying electrical energy in the microwave or radio frequency (RF) band. In particular, microwave thermokeratoplasty may employ a near field microwave applicator to apply energy to the cornea and raise the corneal temperature. At about 60° C., the collagen fibers in the cornea shrink. The onset of shrinkage is rapid, and stresses resulting from this shrinkage reshape the corneal surface. Thus, application of heat energy according to particular patterns, including, but not limited to, circular or annular patterns, may cause aspects of the cornea to flatten and improve vision in the eye, without resorting to surgical intervention.